High sensitivity hydrophones are needed to detect borehole pressure noise in the 1 kHz frequency band. Measurements conducted at various sites show that seismic noise level in borehole drops rapidly as frequency increases (-12 dB per octave). In a quite environment, the measured rms pressure noise level is 2 mPa around 1 kHz; a crosswell system working in this frequency range will take full advantage of low seismic noise level. Moreover, part of borehole seismic noise propagates as tube waves so that noise reduction is expected by array filtering techniques. In case of a noisy environment such as producing pumps near the receiving well, special attention should be paid to pumping activity within a range of 150 m.

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